The effect of exposure condition on the degradation behavior of magnesium rich coatings

We evaluated magnesium rich epoxy polyamide primers under different environmental exposure conditions. The purpose was to highlight differences in deterioration of these types of coatings as a function of exposure condition. We compared data for samples under constant immersion in dilute Harrison's solution (DHS-CI) to identical samples exposed to 90% relative humidity (90% RH). EOCP, XPS and SEM analysis of the coatings supported our findings that the samples under DHS-CI undergo rapid dissolution and deterioration compared to the 90% RH samples. The difference was that the latter were able to form carbonate corrosion products, which are known to provide additional passivating protection.